1. Technical Field
The present invention generally relates to textured crystalline silicon surfaces and methods of producing them. More particularly, the present invention relates to textured crystalline solar cells and methods of their fabrication.
2. Background Information
A critical step toward an enhanced efficiency in sunlight-to-electricity conversion through photovoltaic action is to minimize the reflection of sunlight from the surface of solar devices. This is of particular importance for solar cells based on silicon [Si] crystals, the dominant material in today's photovoltaic market. Si has a high refractive index, causing the reflection of more than 35% of infrared-to-ultraviolet light from a polished Si surface. There are two major approaches to achieving antireflection of Si solar cells. Most commercial cells are coated with quarter-wavelength thin films, but these quarter-wavelength thin film stacks reduce light reflection only for a narrow range of wavelengths and incident angles. Better performance has been achieved with a higher level of sophistication in thin film deposition and materials processing, as exemplified by a multilayer graded-index antireflection coating. A generally less sophisticated method for enhancing light trapping in solar cells relies on the formation of textured surface structures. Anisotropic wet chemical etching to form pyramids in crystalline silicon is a commonly used method for surface texturing, but it cannot be extended for thin film solar cells due to large dimensions of the created textures. Recent work has shown that the creation of surface structure arrays in the form of inverted pyramids or protruding columns, with sizes comparable of sunlight wavelengths and depths of a few microns, can result in a low reflectivity (<5%) over a broad spectral range. However, the fabrication of such surface texture structures requires multiple materials processing steps involving lithography, masking, thin film deposition and anisotropic etching of Si with chemical solutions, reactive ions and even femtosecond lasers, which are neither adequate for large-volume production nor economically viable.
The high production cost and the low manufacturing capacity in the fabrication of Si solar cells remain the obstacle to their terrestrial applications. Thus, a need exists for a cost-effective method of increasing the efficiency of solar devices.